There are numerous polling techniques currently being used to communicate between controllers and transponders. One such system has been developed in which the individual transponder units all have their individual respective addresses, which differ from each other, and the various alarm or transponder units can reply to the controller when addressed. In this way the controller knows when a transponder has a defect or trouble condition when it does not reply to a normal inquiry, even when no alarm or danger condition is present adjacent the addressed transponder.
In such polling arrangements, the transponders are frequently addressed in sequence. For example, if there are 60 transponders connected over a single communication path to a controller, the first transponder is addressed and given time to reply, the second is then addressed, and so forth through the entire 60 units. In this way the controller is continually checking on the operability as well as the alarm status of each of the units.
The aforementioned polling techniques have the following disadvantages. Should an alarm or new input be received by one or more transponder of the system, these polling arrangements require that the system continue interrogating each unit of the system, reset and then interrogate the system again in order to detect that one of the units has received a new input. Although this time period may only be a few seconds, such seconds are precious during most alarm and life safety crises.
One attempt at overriding the normal polling sequence when a high priority message is initiated at a given transponder is set forth in U.S. Pat. No. 4,742,335 (Vogt), which issued on May 3, 1988. This communication system provides a means to define at least one time segment, which occurs at a predetermined time in a polling routine. The time segment may occur at or within the address time of a given transponder, or at a time interval between the addresses or response times of two transponders, or at a time after all the transponders have been addressed and given an opportunity to reply before the next round of polling. During the predefined time segment one or more transponders, from one or more specified groups, can simultaneously reply to the controller regardless of whether the transponders simultaneously have been specifically addressed by the controller. That is, a "public time" is provided to allow nearly instantaneous identification and verification of a high priority interrupt (such as a holdup alarm). However, such "public time" is alloted repetitively on a fixed time basis regardless of whether it is called for due to exigencies of the moment.
The present inventors believe that the above-referenced conventional polling arrangements are, in general, extremely inefficient. Those arrangements require continuous and repetitive polling of each individual transponder, thereby wasting energy that may be in short supply, especially in battery operated systems. Therefore, the present inventors have developed a unique communication system which conserves energy, and which is capable of rapid detection and polling of transponders receiving new inputs.
The present invention also provides many additional advantages which shall becomes apparent as described below.